krishishah
commented
3 years ago In addition to TLVs, various Data Elements (DEs) also consist of subfields and subelements. It would be great to add support to pack/unpack these into the library.
Take an example of DE 3 (Processing Code). The ISO specification describes its structure as such:
However, Spec87 defines it as:
field.NewNumeric(&field.Spec{
Length: 6,
Description: "Processing Code",
Enc: encoding.ASCII,
Pref: prefix.ASCII.Fixed,
Pad: padding.Left('0'),
})Though this is technically correct and will parse successfully, we could extract more granular data from messages by decoding their subfields directly. Note that this is a simplified example - however, they get a lot more complex especially for subelements. To extract subfield data using this library, I propose that we introduce a new field type as such:
package field
// ComplexField represents a Data Element (DE)
// with subelements or subfields within it.
// This struct implements the 'Field' interface.
// Open to naming suggestions.
type ComplexField struct {
spec *Spec
Fields map[int]Field
}
func NewComplexField(spec *Spec) field.Field { ... }
// Logic to implement the 'Field' interface.
func (*ComplexField) Spec() *Spec { }
...The above could also technically be defined separately by the user if we wish to keep such logic out of this library. However, the design pattern above would still require an enhancement moov’s field.Spec struct definition to hold sub-fields as such:
type Spec struct {
Length int
Description string
Enc encoding.Encoder
Pref prefix.Prefixer
Pad padding.Padder
+ Fields map[int]Field
} The great bit about this design is that mapping of Spec.Fields to sub-fields in the ComplexField may then be left to the ComplexField to implement via SetSpec itself. In addition, this would be a non-breaking change.
It may then be used when defining a MessageSpecification as such:
spec := &iso8583.MessageSpec{
Fields: map[int]field.Field{
...
3: field.NewComplexField(&field.Spec{
Length: 6,
Description: "Processing Code",
Pref: prefix.ASCII.Fixed,
Fields: map[int]field.Field{
1: field.NewString(&field.Spec{
Length: 2,
Description: "Transaction Type",
Enc: encoding.ASCII,
Pref: prefix.ASCII.Fixed,
}),
2: field.NewString(&field.Spec{
Length: 2,
Description: "From Account",
Enc: encoding.ASCII,
Pref: prefix.ASCII.Fixed,
}),
3: field.NewString(&field.Spec{
Length: 2,
Description: "To Account",
Enc: encoding.ASCII,
Pref: prefix.ASCII.Fixed,
}),
}
}),
...
},
}
Keen to hear what you guys think of the above. Are you currently able to extract information from fields such as DE 48? I haven't implemented the above myself but I'm open to contributing if required.
vtolstov
alovak
jmptrader
some fields have TLV stuff, do you have plans to add ability to define subfield and parsing capability?